With the widespread use of portable AM/FM receivers, cassette, CD, MP3 players, as well as other consumer electronic devices outputting audio and/or data signals, a need has arisen for more convenient methods for delivering those signals to the system user. Currently, users typically wear headphones that are coupled to the signal-generating device by wires. These wires are inconvenient and possibly dangerous. In the case of portable audio devices, for instance, the devices may be employed while their users are doing other things such as jogging, rollerblading, manual labor, driving, etc. During such activities, wires are susceptible to being tangled up or otherwise providing a hindrance to efficient use. The same is true of wires leading from stationary devices such as a personal computer, car dashboard, or rack mounted stereo. Therefore, as signal generating devices have proliferated, so too has the need to make them convenient. One example of a convenient, hands-free environment was disclosed in U.S. Pat. No. 5,771,441 for a Small Battery Operated Rf Transmitter for Portable Audio Devices for Use with Headphones with Rf Receiver, issued Jun. 23, 1998 to John E. Alstatt (hereinafter referred to as “Alstatt”).
In Alstatt, there is taught a portable RF transmitter that modulates audio signals from an audio source onto an FM carrier and then transmits such signals to an FM receiver mounted on a headset worn by a user. The RF transmitter uses its own ground circuit and the ground circuit of the audio source as two elements of a short dipole. Products, such as the AUDIOBUG™, available from Aerielle Group International, Inc. of Cupertino, Calif., have successfully embodied such a wireless device.
A further example of a solution to the problem of wireless transmission is found where small RF transmitters have been used on electric guitars to transmit audio signals from the guitar transducer to a receiver coupled to a power amplifier. An example of this type of technology is found in U.S. Pat. No. 5,025,704 for a Cordless Guitar Transmitter, issued Jun. 26, 1991 to Richard L. Davis (hereinafter referred to as “Davis”). In Davis, there is taught an electronic device which, when connected to an electric guitar, or other similar stringed instrument, will effect wireless transmission over a selectable frequency of the FM broadcast band. The unit is compact as it uses the metal strings of the guitar as a partial antenna. The unit remains stationary after being plugged into the guitar's input receptacle, and no transmitting portion of the device has to be attached to the musician's belt or guitar strap, or to the musician's person. Furthermore, no antenna extends from the device itself. The device is automatically turned on when plugged in.
As devices providing wireless transmission capabilities have improved and become more convenient and accessible at the consumer level, there has also grown a need to become more efficient in prolonging battery life. Without this efficiency, larger and/or more expensive batteries, or multiple batteries coupled together, are required to drive the transmitters. The alternative has been a drastically reduced battery life. Thus, there has evolved a need for circuits that reduce battery consumption.
Several United States patents reflect proposed solutions to this need, including U.S. Pat. No. 5,636,077, to Kim, which discloses a video recording and reproduction device having an automatic power-saving circuit. The circuit determines the existence of an input video signal and controls system functions accordingly. Video recording and reproduction functions continue if an input video signal is present, and, if no video signal exists and no function key is input for a predetermined period of time, the recording/reproducing actions are halted and power is automatically cut-off.
U.S. Pat. No. 6,441,804, to Hsien, teaches a wireless cursor control system that includes a pointing device and a receiver. The pointing device has a controller for receiving user input and for providing a control signal, and a transmitter that includes an antenna and a high frequency modulator coupled to the controller for receiving the control signal and for generating an output signal for transmission via the antenna. The high frequency modulator includes a variable frequency modulator circuit for selectively changing the frequency deviation of the control signal, and a high frequency circuit for increasing the frequency deviation of the control signal to produce the output signal. The receiver has an antenna that receives the output signal, and a demodulation circuit for demodulating the received output signal. The transmitter circuit includes a power saving circuit coupled to the high frequency modulator and controller and detects whether controller has received any input from a button circuit. If no input has been received by the controller for a predetermined time period, the power saving circuit automatically switches the transmitter into a power-saving mode by disconnecting the RF amplifier and the buffer circuit. In the power-saving mode, the button circuit, clock generator, and controller are on, and the remaining circuits are deactivated. User activation of any of the buttons of the button circuit causes the transmitter to come out of the power-saving mode.
U.S. Pat. No. 6,529,067 to Uen shows a power saving device for a wireless pointer including a first resistor, a second capacitor, a signal generation circuit, a bias control circuit including an n-type channel MOSFET having a drain connected to the signal generation circuit at a second node for driving the signal generation circuit, a switch having one end connected to an n-type channel MOSFET gate at a first node, a semiconductor having an anode connected to the first node gate and a cathode connected to the positive terminal of the power source, and a first capacitor in series connection with the semiconductor means. When the wireless pointer is inoperative, the switch opens automatically to cause the leakage current of the reverse biased semiconductor to charge the first capacitor. When the switch is closed, the first capacitor discharges completely and cuts off the n-type channel MOSFET. The charging and discharging decrease current consumption in a standby mode.
U.S. Pat. No. RE37,884 to Chen discloses a transmitter-receiver system including a transmitter unit installed in an audio equipment, and a receiver unit installed in an earphone, wherein the transmitter unit includes an automatic electric level regulator to regulate the electric level of the output signal of audio equipment to a predetermined range, a power control circuit controlled by the output signal of the audio equipment to provide the necessary working voltage, and an inductance antenna to transmit output signal from the audio equipment to the receiver unit. The receiver unit is of low working voltage design, including an automatic 24-time frequency divider circuit to effectively discriminate left and right sound tracks, and an auto-shut off circuit to automatically cut off power supply when the audio equipment does no work. The transmitter unit and the receiver unit further use a respective dual oscillation frequency regulating circuit consisting of an oscillating transistor, a dielectric resonator, and two variable resistors for regulating the range of the frequency.
The foregoing patents reflect the current state of the art of which the present inventor is aware. Reference to, and discussion of, these patents is intended to aid in discharging Applicant's acknowledged duty of candor in disclosing information that may be relevant to the examination of claims to the present invention. However, it is respectfully submitted that none of the above-indicated patents disclose, teach, suggest, show, or otherwise render obvious, either singly or when considered in combination, the invention described and claimed herein.